1. Field of the Invention
The present invention relates to a seat back structure of a vehicle seat having a pair of hinged points each being de fined on the respective right and left sides thereof, with a locking mechanism equipped therewith, wherein the seat back of the seat is rotatable or foldable about those hinged points relative to a seat cushion thereof. Particularly, the invent ion is directed to the seat back structure of this kind of hinged vehicle seat, wherein the seat back, when in a normal upright state, serves as a partition wall between a driver and passenger cabin section and a luggage loading section in a cabin space of a vehicle.
2. Description of the Prior Art
A vehicle with one interior space only, or a minivan or van type of automobile, is provided with one continuous spacing in its interior by combining together a cabin space where a driver and passengers can sit on their own seats and a load-carrying spaces where luggage and articles can be loaded. In this sort of vehicle or automobile, a seat back of a seat nearest to the load-carrying space (i.e. a seat back of a rear seat nearest thereto) functions as a partition wall between the cabin and load-carrying spaces.
In most cases, such seat (rear seat), whose seat back may serve as the partition wall, is of such a hinged-seat type that allows its seat back to be foldable about a hinge point relative to its seat cushion, so that a driver or passenger can fold the seat back downwardly onto the seat cushion to thereby enlarge the load-carrying space of vehicle or automobile for accommodation of a large size of luggage or article that can not be placed only in the load-carrying space limited by the seat back.
Typically, as understandable from FIG. 1, the hinged seat has a pair of hinged points (as at 16L and 16R), each being defined on the respective right and left lateral sides of seat at a juncture between the seat back and seat cushion, and is also equipped with a pair of locking mechanisms (at M and M), each being operatively coupled with those two hinged points, respectively. As known typically, a connecting rod (at 12) is connected between the pair of locking mechanisms, so that the two locking mechanisms may be operated in a synchronized manner for locking and unlocking of the seat back by applying one operative force thereto. The connecting rod is normally formed with a generally crank-like portion (at 12a). This connecting rod crank-like portion is oriented rearwardly of the seat cushion frame (26) in a relatively upward direction so as to avoid contact with a buttocks or waist portion of an occupant sitting on the seat, which can be seen from FIG. 1.
In such conventional seat back construction, however, when a great external force or load is applied to the above-stated van type of vehicle or automobile, a luggage or articles loaded in the load-carrying space will strongly clash against the rear side of seat back under the inertia, exerting an impact load upon the crank-like portion of connecting rod, with the result that the connecting rod will be rotated in an undesired unlocking direction to actuate the locking mechanism to unlock the seat back. Hitherto, to solve this problem, it has been proposed to provide a rigid cover and a reinforcing tubular member over the connecting rod to protect the same against the great impact load given from the luggage or articles. But, such cover and reinforcing members require a rigidity sufficient to withstand the great impact load, and thus will lead to a large increase of their thickness, sizes, and costs involved. Additionally, to insure the attachment of those rigid members over the connecting rod will make much complicated the peripheral fittings and seat arrangements, which might possibly impair the cushiony effect of foam padding surrounding them all, resulting in a poor seating touch thereof.